diff --git a/src/Common/Order.php b/src/Common/Order.php
index ea37b9e..9b4b76e 100644
--- a/src/Common/Order.php
+++ b/src/Common/Order.php
@@ -52,7 +52,7 @@ public static function withDispatchNumber(string $DispatchNumber): Order
         ]);
     }
 
-    public static function withNumberAndDate(string $Number, \DateTimeInterface $Date): Order
+    public static function withNumberAndDate(string $Number, \DateTimeInterface $Date = null): Order
     {
         return Order::create([
             'Number' => $Number,
diff --git a/tests/Serialization/OrderTest.php b/tests/Serialization/OrderTest.php
index 461779d..d10623b 100644
--- a/tests/Serialization/OrderTest.php
+++ b/tests/Serialization/OrderTest.php
@@ -164,6 +164,17 @@ public function test_can_serialize_with_delivery_surcharge()
   <DeliveryRecipientCostAdv Threshold="2000" Sum="150" VATRate="vat10" VATSum="45.906"/>
   <AddService ServiceCode="30"/>
 </Order>
+', $order);
+    }
+
+    public function test_order_with_number_only()
+    {
+        $order = Order::withNumberAndDate('ORD-123');
+
+        $this->assertSame('ORD-123', $order->getNumber());
+
+        $this->assertSameAsXML('<?xml version="1.0" encoding="UTF-8"?>
+<Order Number="ORD-123"/>
 ', $order);
     }
 }